Alkali metal ion-decorated cyclo[18]carbon molecular wheels for enhanced hydrogen storage: A DFT study

Efficient and lightweight hydrogen storage materials are crucial for sustainable hydrogen energy. Density functional theory (DFT) was employed to investigate H 2 storage on Li + , Na + and K + decorated cyclo[18]carbon (C 18 ) molecular wheels. The positively charged alkali metal ions generate polarized adsorption sites that interact with H 2 through electrostatic attraction and charge-induced polarization. Each decorated C 18 system can adsorb up to 15H 2 molecules, achieving gravimetric capacities of 11.93 wt% for Li + @C 18 , 11.22 wt% for Na + @C 18 , and 10.59 wt% for K + @C 18 . Favorable average and negative successive adsorption energies confirm energetically viable H 2 uptake. Natural population analysis, QTAIM, NCI, RDG and charge-density-difference analyses indicate that adsorption is dominated by weak closed-shell noncovalent interactions and charge-induced polarization. QTAIM results reveal linear correlations between electron density and adsorption strength. Temperature-pressure analysis and AIMD simulations at 300 K demonstrate dynamic H 2 retention and desorption. Overall, alkali-metal-ion decorated C 18 , particularly Li + @C 18 , shows potential for high-capacity hydrogen storage.